A comprehensive review of publications about kelp and fucoids from New Zealand and subsequent experiments on the early life stages of Hormosira banksii.

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Theses / Dissertations
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Thesis discipline
Biological Sciences
Degree name
Master of Science
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Edmunds, Nicolette Rene

Kelp (Laminariales) and fucoids (Fucales) are canopy-forming macroalgae that cover ca. 25% of the world’s coastlines, including many rocky coastlines throughout New Zealand. Marine forests, dominated by kelp and fucoids, are highly biodiverse and productive ecosystems that provide ecosystem functions, such as nutrient and carbon sequestration and habitat for marine species. However, seismic uplift, urbanization, warming, heatwaves, invasive species, eutrophication, coastal darkening, sedimentation, and elevated grazing pressure have reduced their vertical and horizontal distributions, globally and in New Zealand, motivating calls for protection and restoration. Kelp and fucoids have been studied in New Zealand since the 1930s but their research has not yet been systematically reviewed. Here I reviewed published kelp and fucoid research from New Zealand using Scopus searches, and extracted data about spatial locations, elevations, temporal patterns, study species, and study topics (Chapter 2). Data extractions from 430 papers showed that most kelp and fucoids were studied in central New Zealand, in the shallow subtidal zone (<30 m), over relatively short time scales (<2 years) and predominately in a single summer season. Furthermore, most studies were done on a multi-species community level typically showing distribution and abundance data. Ecklonia radiata and Durvillaea antarctica were the most studied kelp and fucoid species, respectively. I also identified a key research gap arising from few published studies on the early life history of fucoids – a research topic that is important for future protection and restoration projects. The systematic review was therefore followed by factorial laboratory experiments to determine optimal conditions to induce gamete release and grow zygotes of fucoids (Chapter 3). Experiments focused on reducing contaminants and specifically test for the relative importance of (a) temperature and heat stress on gamete release, (b) gamete solution-concentration and substrate types, slope, and rugosity on zygote settlement and (c) temperature, shading, fertilization, and competition with diatoms (through GeO2 addition) on germling growth and sizes. The first experiments compared propagule release between Hormosira banksii and other fucoids, but only Hormosira successfully produced zygotes that grew successfully on different substrates. Hormosira was therefore studied in follow-up experiments. First, I found that the release of Hormosira gametes and settlement of zygotes was greatest (when pooled over crossed test factors) at high zygote solution concentration (this single factor explained 10% of the data variability), at short stress duration of the parents (7%), at high temperature stress of the parents (6%), and when the slope of substrate slides was zero (2%) (there was no effects of slide rugosity). Second, in a longer 6-week zygote growth experiment, I found that germling densities were greater in fertilized aquaria (this single factor explained 21% of the data variability), without addition of GeO2 (8%, supposed to inhibit competing diatoms), and on Hardiflex substrates (7%, compared to slide substrates). However, adding shade cloth at two different temperatures (18 vs. 23°C) did not affect densities. Third, I found that factorial analysis on germling sizes was relative similar to the described analysis on densities. Finally, when evaluated across the different factorial experiments, only few higher order interactions were significant, and the significant interactions explained little of the data-variability, mainly varying in magnitude - not direction. This result suggests that effects on early life stages of Hormosira, by different environmental stressors, generally are additive. In conclusion, my work identified (a) key gaps to stimulate new kelp and fucoid research, e.g., associated with early life histories and restoration, and (b) environmental conditions that maximize success of early Hormosira life stages, which could improve future restoration aimed to rebuild and restore decimated intertidal Hormosira beds.

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